Ubuntu doesn't boot from active RAID 5 array after failed OS update

Hamid Gadirov

12/2/23, 3:37 PM

Some time ago I tried to upgrade Ubuntu from 16.04 to 18.04 via ssh from a remote PC. The system is configured as a RAID 5 array (with 3 physical drives). After that, I lost the ssh connection and later I found that the PC no longer boots Ubuntu on the local hardware.

I mounted the RAID array via sudo mdadm --assemble /dev/md0 from a live USB. This worked, which suggests that RAID array has not been damaged. I thought the issue might be related to grub so I tried to reinstall it via sudo grub-install /dev/md0 but that showed an error:

grub-install: error: failed to get canonical path of '/cow'

After executing sudo touch /cow, sudo grub-install /dev/md0 command outputted

Installing for i386-pc platform.
grub-install: error: unknown filesystem.

I already tried to run sudo dpkg-reconfigure grub-pc and then select /dev/md0 but there was no output and the system is still not bootable. I am not sure what needs to be done at this point.

How can I make it so that the system boots to Ubuntu on the RAID array again? Is there perhaps a way to repair GRUB from the live USB so that we can boot to the operating system again? Alternatively, is there a way to check the state of Ubuntu on the RAID array to see if there is an error that was caused by the incomplete update?

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